Sty noise (4)
I believe the answer is:
oink
'sty noise' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for oink that I've seen before include "it might be in a pen one hears" , "Piggish noise" , "behave like a pig" , "Pig's grunt" , "Sound made by a pig" .)